Strange mesh deformation when using the action editor?
While you can manually add an armature modifier to an object and set it up to work, the most common method is to start by setting the armature as the parent of the mesh object. While the armature is the parent, moving it in object mode will also move the mesh with it, keeping things aligned.

Once an armature is setup to deform a mesh object moving one of them without the other gives a weird deformation as seen in your screenshot. Even if the armature is the parent you can move the mesh object by itself and get the same bad deformation.

The further apart you move the armature and the mesh the worse the distortion is.

If you have the armature as the parent of the mesh then be sure to move the armature and not the mesh.

If you don't want to use parenting then you need to make sure you move both the armature and the mesh together.

Also scaling one without the other can produce the same result.

That applies to moving the two objects in object mode not moving the armature in pose mode.

One thing to watch is if you use automatic keyframing, you need to make sure you turn it off when you finish animating.